Without limiting the scope of the invention, its background is described in connection with aircraft. Based on a classical helicopter configuration improvements in helicopter productivity have been, at best, only incremental. A classical helicopter configuration includes certain fundamental limitations that hamper improvements, e.g., retreating blade stall, blade loading, advancing blade tip Mach number, and the large increases in power that are required with increased speed. These physical limitations contribute to increased vibration resulting poor ride quality and reduced component life. In addition, certain physical limitations lead to increased size and weight.
The classical approach to this problem is to develop helicopters in which these configuration limitations are addressed via ancillary devices, such as wings, additional engines, and propellers. Incorporation of these approaches, due to their increased complexity and weight, reduces the economic load carrying capability of the helicopter and raises questions as to the safety of operation of the helicopter and its long term reliability. Although the development of compound helicopters with wings, additional engines, and propellers represents significant improvements in helicopter productivity, considerable shortcomings remain.